In the construction of aircraft, in particular, different metallic and/or non-metallic components are increasingly connected to one another by means of adhesive bonding in order to simplify the production process and to reduce the weight in relation to conventional riveted, screwed and/or welded connections. However, these adhesive bonds need to be separated again in order to repair, exchange, scrap or recycle thusly connected components. This process frequently is relatively difficult because the adhesive bonds build up a high adhesive force during their period of use and therefore can only be separated by applying high forces or high temperatures or with the aid of chemical agents, wherein the connected components are frequently damaged or even destroyed. Adhesive compositions for separable adhesive bonds are known in different variations. These compositions normally consist of an adhesive matrix (also referred to as binder matrix) and an expansion material dispersed therein. If the connected components should be intentionally separated, the expansion materials expand due to the input of energy in order to thusly weaken the adhesive bond and to simplify the separation of the components.
DE 199 61 940 A1 discloses an adhesive composition, the binder system of which incorporates substances that can be thermally activated and are able to trigger a debonding process. These thermally activatable substances are solid at room temperature and homogenously distributed in the binder matrix in the form of fine particles. When exposed to heat, these substances should cause swelling of the binder matrix, undergo a phase transformation, be decomposed and/or produce gases or water vapor. Adhesive compositions for realizing adhesive bonds that can be separated again due to a pyrolysis of incorporated expansion materials are furthermore described in U.S. Pat. No. 3,615,960, WO 00/40648 A1 and DE 10 2004 050 949 A1.
In their cured state, however, these adhesive compositions frequently only have a low stability when they are subjected to high temperatures, water or chemical attacks such that the expansion agent may prematurely expand and already lead to inadvertent weakening of the adhesive bond during its period of use. In addition, the curing reaction of these adhesive compositions frequently is already impaired because a reaction between the expansion material and other components of the uncured adhesive matrix or the adhesive matrix itself may already occur during the storage of the composition or during the curing process. Furthermore, the separation of the adhesive bonds and the connected components frequently requires high temperatures over a long period of time such that these components may be overheated and therefore damaged or destroyed.
Consequently, there still is a need for adhesive compositions for separable adhesive bonds that have a sufficient chemical and thermal stability in the uncured state, as well as in the cured state. Furthermore, these adhesives should develop a sufficient adhesive force during their period of use in adhesive bonds, but also be easily separable on demand.